Sulfur-containing esters of silicon acids



United States Patent SULFUR-CONTAINING ESTERS OF SILICON ACIDS Rupert C. Morris, Berkeley, and John L. Van Winkle,

San Lorenzo, Calif., assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware No Drawing. Application July 30, 1952,

. Serial No. 301,799

9 Claims. (Cl. 260448.8)

This invention relates to new organic esters of silicon acids. More particularly, the invention relates to novel sulfur-containing esters of silicon acids, and to their utilization, particularly as synthetic lubricants and hydraulic fluids.

Specifically, the invention provides new and valuable esters of acids of the group consisting of silicic acid and substituted derivatives thereof, and alcohols containing at least one thioether linkage, polysulfide linkage, sulfinyl or sulfonyl radical attached to carbon atoms in an openchain portion of their molecule.

It is an object of the invention to provide a new class of esters of silicon acids that are particularly useful and valuable in industry. It is a further object to provide sulfur-containing esters of silicon acids that are particularly valuable as synthetic lubricants and non-flammable hydraulic fluids. It is a further object to provide novel sulfur-containing esters of silicon that have viscosities within the range needed for high temperature combustion It is a further object to provide novel esters of engines. silicon acids that have superior load-carrying properties; It is a further object to provide novel sulfur-containing esters of silicon acids that exhibit high viscosity indices as well as high flash points. It is still a further object to provide novel esters of silicon acids that have good stability when exposed to oxidizing conditions in the presence of metals. It is afurther object to provide synthetic lubricating compositions that are suited for use with turbojet engines. Other objects and advantages of the invention will be apparent from the following detailed description thereof.

It has now been discovered that these and other objects may be accomplished by the novel compounds of the invention comprising esters of acids of the group consisting of silicic acid and substituted derivatives thereof, and alcohols containing at least one thioether linkage, polysulfide linkage, sulfinyl or sulfonyl radical attached to carbon atoms in an open-chain portion of their molecule. These particular esters have been found to possess surprisingly superior properties as synthetic lubricants and hydraulic fluids. They are particularly suited for use as lubricants for engines which are subjected to high temperatures, such as combustion turbine engines and particularly those of the prop-jet type as they generally have viscosities within the range desired for this type of lubricant, e. g., they have viscosities at 65 F. generally below about 5000 cs. and a viscosity of more than 3.0 cs. at +210 F. In addition, the esters possess surprisingly high viscosity indices, e. g., VIs ranging from 150 to 250, as well as very high flash points, e. g., flash points varying from 550 F. to 700 F., and are thus ideally suited as high temperature lubricants and non-flammable hydraulic fluids. The esters of the invention also generally possess unusually high load-carrying properties and are of value as extreme pressure lubricants. Furthermore, the esters have low pour points and low corrosivity as to metals as iron, aluminum and cadmium and can be used as lubricants and hydraulic fluids in combination with these ice ' 2 metals without the addition of conventional pour point depressants and oxidation inhibitors.

The sulfur-containing alcohols used in producing the novel esters of the invention comprise those alcoholshaving at least one member of the group consisting of a thioether linkage, i. e., a S linkage, a polysulfide linkage, such as SS linkage, a sulfinyl radical, i. e., a SO radical, or a sulfonyl radical, i. e., a SO2 radical, attached to carbon atoms, and particularly aliphatic carbonv atoms, in an open-chain portion of the alcohol molecule. These alcohols may be monohydric or polyhydric, i. e.,

may possess two, three, four or more hydroxyl groups,

and may be aliphatic, aromatic or heterocyclic and saturated or unsaturated. The alcohols preferably contain at least 5 and more preferably at least 7 carbon atoms.

The thioether substituted monohydric alcohols may be,

exemplified by the following: 4-thiaoctan-1-ol, i. e., C4H9SC3H6OH, 3-thiadodecan-1-ol, 3,7-dithiadodecan-1- o1, 3,3-dibutyl-S-thiatetradecan-1-01, 7-cyclohexyl-4-thiaheptanl-ol, 6-phenyl-4-thiahexan-l-ol, 6-methyl-5-thia-3- hepten-l-ol, 2-butyl-7-thiaoctadecan-1-01, 7-thiahexadecan- 1-01, 7-cyclopentyl-4-thiatridecan-1-01, and Z-chloromethyl-7-thia-8-octadecen-l-ol. Particularly preferred alcohols of this type are the aliphatic monohydric alcohols containing a single thioether linkage and from 5 to 20 carbon atoms, and more preferably the thiaalkanols con-' taining from 5 to 16 carbon atoms. Of special interest for the preparation of synthetic lubricants are those alcor hols having the sulfur atom and the hydroxyl group attached to primary aliphatic carbon atoms. 1 t

The above-described alcohols may be prepared by a. variety of methods. They may be prepared by reacting an organic halide with an alcohol containing a sulfhydryl group, or alternatively by reacting a halo-substituted alcohol with a sulfhydryl-containing compound, preferably in an alkaline solution or in the presence of a catalyst, such as sodium methoxide. The alcohols may also be prepared by reacting a mercaptan with a carbonyl-containing alcohol, such as gamma-ketobutanol. I

The preferred method for preparing many of the abovedescribed alcohols, however, comprises reacting a mercaptan with an unsaturated alcohol.

strong inorganic acid.

The polyhydric thioether-containing alcohols used in the preparation of the novel esters of the invention may be exemplified by the following: bis(2-methyl-4-hydroxy butyl) sulfide, bis(2-ethyl-5-hydroxyhexyl) sulfide, bis(2- hydroXypropyl) sulfide, bis(3-ethyl-4-hydroxyoctyl) sulfide, 5-hydroxy-4-thiaoctan-l-ol, 7-hydroxy-2,4-dithiadotheir resulting better adaptability to important uses, e. g.,,

synthetic lubricants, etc., are those polyhydric alcohols having the sulfur atom and the hydroxyl groups attachedto primary aliphatic carbon atoms.

Higher molecular alcohols produced by the polymerization of the dihydroxy-substituted thioethers may also be used to prepare the novel esters. Such alcohols pref-v erably have the general formula HOR-SROH where R represents a saturated hydrocarbon radical, such as an alkylene group of from two to three carbon atoms which may be further substituted with alkyl groups, such as containing from 1 to 4 carbon atoms, and it is an integer greater than 1, and preferably from 1 to 5.

The above-described polyhydric thioethercontaining al-v This may be ac-. complished in the presence of actinic light or in they presence of an organic peroxide and a metal salt of a cohols may be prepared by a variety of methods. They may be prepared, for example, by adding hydrogen sulfide to unsaturated alcohols, such as allyl alcohol in the presence of a catalyst, such as an amine, a metallic oxide, or a peroxide. The dithioether-substituted polyhydric alcohols may be prepared by adding dimercaptans, such as ethanediol, butanedithiol, benzenedithiol, and the like to unsaturated alcohols in the presence of the above-described catalysts. Other alcohols, and particularly those of the asymmetric type, may be prepared by adding epoxide-contaming materials to mercapto-substituted alcohols.

The pol-ysulfide-containing monohydric alcohols used in preparing the novel esters of the invention may be exemplified by the following: 4,5dithiaoctan-1-ol, i. e., C4HaSS sHeH, 6-phenyl 4,5 dithiaheptan 1 ol, 4- methylfl,8 dithiadodecan-lrol, -cyclohexyl-7,S-dithiatctradecan-l ol, 3,3-dibutyl-5,6dithiadodecan-l-ol, 3-butyl- 7,8-dithiadodecan-1-ol, and 4-chlorobutyl-7,S-dithiapentadecan-Lol. Preferred alcohols of this type comprise the aliphatic alcohols containing a single -SS- group and from 6 to carbon atoms. Particularly preferred alcohols are those of the formula RSSRlOH wherein R is an aliphatic hydrocarbon radical and R1 is an aliphatic hydrocarbon bivalent radical and the entire alcohol molecule contains from -6 to 14 carbon atoms.

The polysulfide containing polyhydric alcohols may be exemplified by the following: bis(2-methyl-4-hydroxybutyl) disulfide, bis(Z-ethyl-S-hydroxyhexyl) disulfide, bis(2 -hydroxyethyl) disultide, 6-hydroxy-4,S-dithiaheptanl-ol, 6-hydroxy 4,5 dithiadodecan l 01, 12 hydroxy- 6,7,9,lO tetrathiatetradecan-l-ol and 5-hydroxy-6-cyclohexylAj-dithiadccan-l-ol. Preferred polyhydric alcohols of this type comprise those of the formula HORSSROH and those of the formula HORSSRSSROH wherein each R is a hydrocarbon bivalent radical, and preferably an aliphatic hydrocarbon bivalent radical, and the entire alcohol molecule contains from 6 to 20 carbon atoms.

Theabove-described polysulfide-containing monohydric alcohols are preferably prepared by reacting an organic monohalide, such as ethyl halide with sodium polysulfide and a halosubstituted alcohol, such as chloropropanol. The polysulfide-containing polyhydric alcohols are preferably prepared by reacting an organic polyhalide such as propylene dichloride with sodium polysulfide and the halosubstituted alcohol. In this case, the molecular weight of the resulting alcohol maybe controlled by regulating the proportions of reactants.

The sulfinyl and sulfonyl-substituted monohydric alcohols used in the preparation of the novel esters of the invention may be exemplified by 3,3-dioxo-3-thiaoctan-l-ol, i. e., CsH11SOzC2H4OI-I, S-isopropyl-4,4-dioxo-4-thiaoctanl-ol, 3-oxo-3-thiaoctan-l-ol, 5,5-dioxo-5-thiadodecan l-ol, 2-chlorohexyl-4-oxo-4-thiaoctan-1-01, Z-rnethyl 4 butyl- 5,5-dioxo-5-thiatetradecan-l-ol, Z-methyl-4-butenyl-5-oxo- S-thiatetradecan-l-ol, and Z-methyl 4 butyl 5,5 dioxo- S-thiadodecan-l-ol. These alcohols may also be described in terms of the sulfonyl and sulfinyl radicals, i. e., 3,3- dioxo-thiaoctan-l-ol may be described as 3-sulfonyloctan-l-ol. Preferred alcohols of the aforedescribed type are the monohydric alcohols containing no more than 20 carbon atoms and having from 1 to 3 sulfonyl radicals attached to aliphatic carbon atoms. Particularly preferred are the alcohols of the formula RSOzRrOH wherein R isa hydrocarbon radical and R1 is an aliphatic hydrocarbon bivalent radical and the entire alcohol molecule contains from 6 to 14 carbon atoms. Also of special interest, particularly because of the higher stability of the resulting esters, and their resulting better adaptability for use as lubricants, are those alcohols having the sulfinyl or sulfonyl radical and the hydroxyl group attached to primary aliphatic carbon atoms.

The sulfinyl and sulfonyl-substituted polyhydric alcohols may be exemplified by the following: bis(2-meth yl-4- hydroxybutyl) sulfone, bis(2-methyl-5-hydroxyhexyl) sulfone, bjs(2-hydroxypropyl) ,sulfoxide, bis(2-h yd. oxyoctyl) sulfone, bis(2-butyl-4-hydroxyamyl) sulfoxide, S-hydroxy- 4,4-dioxo-44hiahexan-l ol, 5-hydroxy-4-oxo-4-thiaoctanl-ol, 7-hydroxy-4,4-dioxo-4-thiadodecan-l-ol, 5,7-dihydroxy-4,4-dioxo-4-thiadecan-l-ol, and 7-hydroxy-4,4-dioxo-4-thiadecan-1-ol. Preferred alcohols of this type are the aliphatic polyhydric alcohols containing from 1 to 3 sulfinyl or sulfonyl radicals attached to aliphatic carbon atoms and containing from 6 to 18 carbon atoms. Particularly preferred are the alcohols of the formula HORSOROH, HORSOzROH, HORSORSORQH' and" HORSOZRSOZROH wherein R is a bivalent aliphatic hydrocarbon radical and the total alcohol molecule contains no more than 14 carbon atoms.

The above-described sulfinyl and sulfonyl alcohols may be prepared by any suitable method. They are preferably prepared by oxidizing the corresponding :thioether alcohol. Complete oxidation of the thio groups produces the sulfonyl alcohols, while partial oxidation produces the corresponding sulfinyl alcohols.

The oxidation of the thioether alcohols maybe effected by any of a large number of oxidizing agents, such as hydrogen peroxide, sodium perbenzoate, permanganates,

bromine, fuming nitric acid, chromic acid, and perbenzoic acid. The oxidation may also be effected by treating the thioether alcohols with molecular oxygen, preferably in the presence of catalysts. agent to be employed will vary over a considerable range. If the sulfinyl alcohol is the desired product it is generally desirable to react the thioether alcohol with an approximately chemical equivalent amount of the oxidizing agent, i. e., the amount of agent required to furnish 1 atom of oxygen for every thioether linkage to be oxidized. sulfonyl alcohols are desired, it is generally desirable to react the thioether alcohols with at least twice the chemical eouivalent amount of the oxidizing agent.

It is also possible to utilize partial esters of the abovedescribed polyhydric sulfur-containing alcohols in the preparation of the novel esters of the invention. The par tial esters are particularly preferred when the resulting esters of the silicon acids are to be utilized for special lubricating purposes.

toluic acid, caproic acid, caprylic acid, and the like.

The acids used in the preparation of the novel esters. of the invention may be any of the silicon acids, such as silicic acid, disilicic acid, trisilicic acid, and the like. Sub

stituted derivatives of these acids, e. g., those acids where in at least one but not all of the OH groups have been repreparation of these esters.

substituted silanes, such as methaneorthosiliconic acid (CI-I3Si(OHa)') or methanetrihydroxysilane, phenyltrihydroxysilane, butyltrihydroxysilane, cyclohexyltrihydroxy silane, dimethyldihydroxysilane, and dibutyldihydroxysilane. Partial esters of the above-described acids and other al-i cohols may also be used for the preparation of the novel esters of theinvention. Suitable derivatives of this type may be exemplified by dibutoxydihydroxysilane, phenoxy trihydroxysilane, allyloxytrihydroxysilane, and diisopro-.

pyldihydroxysilane. Preferred acid esters are those where in'one of the hydrogen atoms on the hydroxyl group of the aforedescribed silicon acids has been replaced by an alkyl, alkenyl or aryl radical containing no more than 8 carbon atoms.

The novel esters of the invention are theoretically derived by esterifying any one of the above-described acids or acid esters with any one of the above-described sulfurcontaining alcohols. A single sulfur-containing alcohol may be used in the es rification, or a mixture of tw ormote of such alcohols may be tilized. IIJ-SDmC instances,

The amount of the oxidizing If the Preferred partial esters to be used for this application are the esters of the above-noted poly-' hydric alcohols and alkanoic and alkanedioic acids, such: as acetic acid, phthalic acid, butyric acid, benzoic acid,

the use of a mixture of the sulfur-containing alcohols has been found to give esters having unusual lubricating properties.

The esters derived from the silicon acids and the thioether monohydric alcohols may be exemplified by tetrakis- (7-methyl-4-thiaoctyle) silicate, tetrakis(4,6-diethyl-3- thiaoctyl) silicate, tetrakis(3,6-dithiaoctyl) silicate, tetrakis(3-cyclohexyl-S-thiadodecyl) silicate, dibutoxydi( 7- methyl-4-thiaoctoxy) silane, allyloxy-di(5-thiaoctoxy) silane, dibutyl-di(5-methyl-4-thiadecyloxy) silane. The

esters derived from the thioether polyhydric alcohols may 1 be exemplified by l,6-di(triethylsiloxy) -5-thiahexane, 1,5-

di(tributylsiloxy)-3-thiapentane, 1,8 di(triallylsiloxy)-3,6-

wherein X is a silicon, R is a monovalent aliphatic hydrocarbon radical and R1 is a bivalent aliphatic hydrocarbon radical,- both R and R1 together contain from 5 to 16 carbon atoms, R2 is a hydrocarbon radical, and preferably an aliphatic hydrocarbon radical containing from 1 to 8 carbon atoms, a is at least two and the sum of a and b is equal to the valency of X. Preferred polyhydric alcohol esters are those of the formula:

rat-mm):

wherein R1, X and R2 are as described above and d is equal to 1 less than the valency of X.

The esters derived from the polysulfide-substituted monohydric alcohols and the silicon acids may be exemplified by tetrakis(7-butyl-4,5-dithiaoctyl) silicate, tetrakis(7-methyl-5,6-dithiaoctyl) silicate, tetrakis(6-phenyl- 4,5-dithiahexyl) silicate, diallyloxy-di(7-methyl-4,5-dithiaoctoxy) silane. The esters derived from the polyhydric alcohols of this type may be exemplified by 1,8-di- (triethylsiloxy) 5,6 dithiaoctane, 1,5 di(tributyl siloxy) -3,4-ditbiapentane, 1,8-di triallylsiloxy) -5,6-dithiaoctane, 1,2,6 (trioctylsiloxy) 3,4 dithiaoctane, 1,8 di- (ethoxydibutyl siloxy) 5,6 dithiadodecane, 1,10 di (triethylsiloxy)-6,7-dithiadodecane, a polyester of silicic acid and bis(3-hydroxypropyl) sulfone.

PEferred esters of the invention derived from the polysulfide alcohols are those prepared from the above-described silicon acids and the aliphatic monohydric alcohols'containing a single fi$S group and from 6 to 20 carbon atoms. Particularly preferred are those esters of the formula wherein X, R2,a and b are the same as described above, R is a monovalent aliphatic hydrocarbon radical and R1 is a bivalent aliphatic hydrocarbon radical wherein both R and R1 together contain from 6 to 14 carbon atoms. Preferred polyhydric alcohol esters are those of the formula:

(R2 aXORr-SS-RrOX (R2) d wherein R1, X and R2 and d are described above.

The esters derived from the sulfinyl and sulfonyl-substituted alcohols and the silicon acids may be exemplified by tetrakis( 7 methyl 4,4 dioxo 4 thiaoctyl) silicate, tetrakis-(6-methyl-5,S-dioxo-S-thiooctyl) silicate, tetrakis- (5,5-dioxo-5-thiadodecyl) silicate, tetrakis(2,5-diethyl-6- oxo-6-thiononyl) silicate, dibutoxy-di(7-methyl-4,4-dioxo-4-thiaoctoxy) silane, allyloxy-di(5-oxo-5-thiaoctoxy) 6 silane, dibutyl-di(5-methyl-4-oxo-4-thiadecycloxy) silane. The esters derived from the sulfinyl and sulfonyl-substituted alcohols and the silicon acids may be exemplified by 1,6-di(triethy1siloxy)-5-oxo-5-thiahexane, 1,5-di(tributylsiloxy) 3,3-dioxo-3-thiapentane, 1,8 di(triallylsiloxy)-6-oxo-6-thiaoctane,

1,2,6-tri (trihexylsiloxy) -3 ,3-dioxo-3-thia- I 1,2,6-tri(trihexylsiloxy)-3-oxo- 3 thiahexane, hexane, 1,8-di(trial1ylsioxy)-3-oxo-3-thiadecane.

Preferred esters of the invention derived from the sulfonyl alcohols are those prepared from the above-described silicon acids and aliphatic alcohols containing a single -So2v group and not more than 20 carbon atoms. Particularly preferred are the esters of the formula:

wherein X, R2, a and b are the same as described above, R is a monovalent aliphatic radical and R1 is a bivalent aliphatic hydrocarbon radical wherein both R and R1 together contain from 6 to 14 carbon atoms. Preferred polyhydric alcohol esters are those of the formula:

wherein R1, X, R2 and d areas described above.

Esters coming under special consideration, particularly because of their fine those of the formula:

Si(OY)4 fur-containing alcohol with a halogen-containing deriva-' tive of the desired acid. The esters of silicic acid may be prepared in this manner by reacting the desired alcohol with a silicon tetrahalide, such as silicon tetrachloride or tetrabrornide. The esters of the substituted silicic acids may be prepared by reacting the alcohol with the silicon mono-, dior trichloride derivatives, such as methyltrichlorosilane, butyltrichlorosilane, phenyltrichlorosilane, trimethyldichlorosilane, diethyldichlorosilane, and cyclohexyltrichlorosilane.

The esters of silicon acids may also be prepared by reacting the alcohols with a volatile ester of silicic acid, such as ethyl silicate.

The novel esters of the invention are preferably prepared by reacting the sulfur-containing alcohol with the halogen-containing derivative of the acid, such as silicon tetrachloride, etc. This reaction may be carried out by merely combining the reactants together in a suitable reaction vessel. In many cases, excesive heat is liberated and it is desirable to, conduct the reaction in the presence of a solvent, such as toluene, benzene, and the like. The

reaction may also be regulated by the controlled addition of one reactant, such as the halide, to the other reactant. The reaction is also preferably carried out in the presence of a compound or material which combines with or absorbs the liberated hydrogen halide, such as amine, e. g., pyridine, triamylamine, etc., or other basic-acting substance. On completion of the reaction any amine salt formed by the reaction of the added amine and hydrogen halide may be removed by filtration or other means. The reactants are conveniently employed in substantially the stoichiometrically required amounts, although in the event one reactant is more precious than the other, a moderate excess of the less precious one may be employed to insure high conversion of the other reactant to desired product. The reaction may be carried out at temperatures within the range of about 0 C. to about C. and more preferably between the range of 0 C. to 65 C. In most cases, fractional distillation is the most convenient method for recovering the desired product although it will properties as turbo-jet lubricants are be appreciated that other applicable methods may be used in appropriate cases.

As indicated above, the novel esters of the invention can be used per se as synthetic lubricants and hydraulic fluids. They are also compatible with mineral oils and other components, such as the high molecular Weight esters of the acrylic acid series and may be used in combination therewith to produce other valuable lubricating compositions and hydraulic fluids.

The novel esters of the invention are also valuable as heat transfer agents, grease bases and grease additives, textile lubricants, vulcanizing accelerators, dispersing agents for oils, polishes, and the like. They are also particularly valuable as plasticizers and softeners for resinous materials, such as cellulose derivatives, ureaaldehyde resins, vinyl resins, and the like. The esters of the invention are, in general, compatible with these materials at the normal loadings and give compositions having excellent flexibility over a wide range of temperature, good strength and increased flame retarding properties. In this capacity they may also be used in combination with other plasticizing agents, such as dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, and the like.

To illustrate the manner in which the invention may be carried out the following examples are given. It is to be understood, however, that the examples are for the purpose of illustration and the invention is not to be regarded as limited to any of the specific conditions recited therein. Unless otherwise specified, parts disclosed in the following examples are parts by weight.

EXAMPLE I .(a) This example illustrates the preparation of tetrakis (7-methyl-4-thia-l-octyl) silicate. About 1500 parts of toluene .and 783 parts of 7-rnethyl-4-thia-l-octanol were added to a five liter 4-necked flask equipped with mechanical stirrer, thermometer well, reflux condenser and dropping funnel. The flask was then placed in a cooling bath and an HCl trap attached to the top of the reflux condenser. About 1700 parts of silicon tetrachloride was then slowly added and the reaction mixture stirred. The reaction temperature was maintained at 24*26 C. with the aid of the cooling bath. After the addition of the silicon tetrachloride, the reaction mixture was refluxed for about 3 hours. The mixture was then allowed to stand for 48 hours and anhydrous ammonia bubbled through the charge to neutralize the acidic material present. The mixture was then washed, dried,

and topped at 200 C. (1 mm.) to obtain a light yellow 3 liquid identified silicate.

(b) This portion of the example illustrates some of the superior physical properties of tetrakisU-methyL lthia laoctyl) silicate which makes it particularly adapted for use as a lubricant.

The absolute viscosities of a sample of the tetrakis(7- methylA-thia-l-octyl) silicate at diiierent temperatures are shown in the following table in comparison to those obtained from related esters;

as tetrakis(7-rnethyl-4-thia-l-octyl) The above data indicate that the tetrakis(7-methy1-4* thia-l-octyl) silicate is superior to the above named esters as a turboq'ct lubricant as it has viscosities within the desired range for these lubricants, i. e., below 5,000

cs. at -65 F. and above 3.0 cs. at 210 F.

The load-carrying capacity of the tetrakis(7-methyl-4- thia-l-octyl) silicate was determined by the 4 Ball E.-P. test and a spur-gear test. on a spur-gear machine which consisted essentially of two geometrically similar pairs of gears connected by two parallel shafts. The gear pairs are placed in separate gear boxes, which .also contain the supportingball bearings. One of the shafts consists of two sections connected 1 by a coupling. Loading is accomplished by locking one side of the coupling and applying torque to the other. The results of the two tests are shown in the table below in comparison to results obtained with tetrakis(2-ethylhexyl) silicate:

Table II E. P. Test;

Ester Kilograms Add. Score Load,

Tetrakis(i-methyl--thia-l-octyl) silicate. Tetrakis(2-ethylhexyl) silicate greater than 80. 4050 20.

3,000 R. P. M. pinion speed; ambient temp.; 10 cc.; sec. or higher flow rate.

The VI and flash point of the tetrakis(7-methyl-4- thia-l-octyl') silicate was determined by conventional methods. comparison to results obtained with related esters:

treated With charcoal and the resulting product tested to determine its stability when exposed to oxidizing conditions in contact with various metals according to the method described in Federal Specification VVL-79lD, Test 530.81. In this test, separate samples of ester are tested for resistance to oxidation and corrosion of metals in the presence of copper, magnesium, iron, cadmium and aluminum, by aerating the samples with avigorous stream of gaseous oxygen for 71 hours at room temperature in contact with weighted test strips of the metals. The test strips then are withdrawn and loss in 'weight determined as a measure of the amount of corrosion. The results are shown in the following table.

Thus, under these conditions the ester iS slightly corrosive toward copper and magnesium, but is inert with.

respect to iron, cadmium and aluminum. These results are quite surprising in view of the fact that the ester contained no added corrosion inhibiter as is usually present with the other lubricating compositions.

EXAMPLE II I This example illustrates the preparation and properties of tetrakis(6-methyl-4-thia-l-heptyl) silicate. About 500' parts-of toluene and 225 parts of o methyl-4-thiaheptan" 1-01 were added to a reaction flask similar to the one used The spurgear test was made Spur-gear Test Lb. Beam Load The results are shown in the table below in in Example I above. 51.8 parts of silicon tetrachloride was then added slowly and the temperature maintained at 25-30" C. After the silicon tetrachloride had been added, the temperature was raised to reflux and held there for 3 hours. NH: gas was then passed in for 20 minutes to neutralize the acidic material. The mixture was then washed, dried, and topped at 150 C. (1 mm.). The resulting product was a light yellow liquid identified as tetrakis(6-methyl-4-thiaheptyl) silicate. The sample showed the following analysis; S theory 20.8, found 20.1.

Tests conducted as shown in Example I (b) above indicated that the ester had the following properties:

Viscosity (centistokes):

Esters having related properties are obtained by replacing the 6-methyl-4-thiaheptan-l-ol in the above-described process with equivalent amounts of each of the following alcohols: 2-methyl-4-thiaoctan-l-ol, 3,7-dithiadodecan-l-ol, 3,3dibutyl-S-thiatetradecan-l-ol, 7-cyclohexyl-4.-thiaheptan-1-ol, 6-phenyl-4-thiahexan-1-ol, and 7-methyl-4-thiadecan-1-ol.

EXAMPLE III This example illustrates the preparation of tetrakis- (7-methyl-4,4-dioxo-4-thiaoctyl) silicate. About 1500 parts of toluene and 910 parts of 7-methyl-5,5-dioxo-5- thiaoctan-l-ol (obtained by the oxidation of 7-methyl- -thiaoctanl-ol), are added to a reaction flask as shown in Example I above. 1700 parts of silicon tetrachloride is then added slowly and the temperature maintained at 25-30 C. After the silicon tetrachloride has been added, the temperature is raised to reflux and held there for 3 hours. NH; gas is then passed in to neutralize the acidic material. The mixture is then washed, dried, and distilled. The resulting product is a viscous liquid identified as tetrakis(7-methyl-4,4-dioxo-4-thiaoctyl) silicate. This ester possesses a VI pour point and load-carrying capacity similar to the ester shown in Example I.

Esters having related properties may be obtained by replacing the 7-methyl-4-thiaheptanol in the above process with equivalent amounts of each of the following alcohols: 3,3-dibutyl-5,5dioxo-S-thiatetradecan-l-ol, 7-cyclohexyl-4,4-dioxo4-thiaheptan-l-ol, and 6-phenyl-4-oxo- 4-thiadecanol.

EXAMPLE IV This example illustrates the preparation of dimethyldi-(4-methyl-5-thiaoctoxy) silane. About 130 parts of dimethyldichlorosilane in 600 parts of benzene is slowly added to 750 parts of 7-methyl-4-thiaoctanol. After the mixture has been added, the reaction mixture is warmed to reflux for several hours. NH3 gas is then passed through to remove the acidic material. The resulting mixture is then distilled to recover the desired dimethyldi-(7-methyl-4-thiaoctoxy) silane, a light yellow liquid.

EXAMPLE V This example illustrates the preparation of 1,7-di- (trimethylsiloxy)4-thiahexane.

About 850 parts of 4-thiaheptanediol-1,7 (obtained by adding hydrogen sulfide to allyl alcohol) is added to 600 parts of benzene and the resulting mixture placed in a 4-neck reaction flask. About 108 parts of trimethylchlorosilane is then slowly added to the mixture. After the addition, the reaction mixture is warmed to reflux for about 3 hours and then allowed to stand. NHs is then passed through the mixture to remove the acidic material. The mixture is washed, dried, and distilled. The resulting product is a viscous liquid identified as 1,7-di(trimethylsiloxy)- 4-thiahexane. This liquid has good load-carrying capacity and good stability to oxidation.

Esters having related properties may be obtained by replacing 4-thiaheptanediol-1,7 in the above process with equivalent amounts of each of the following alcohols: bis(2-methyl-4-hydroxybutyl) sulfide, bis(2-hydroxypropyl) sulfone, and 7-hydroxy-4-thiadodecan-1ol.

We claim as our invention:

1. An ester of a thialkanol and an alkyltrihydroxysilane.

2. An ester of silicic acid and a saturated aliphatic hydrocarbon monohydric alcohol containing a thioether linkage attached to aliphatic carbon atoms in an openchain portion of the molecule and containing from 6 to 20 carbon atoms.

3. An ester of a substituted silicic acid Si(R)aOH wherein R is an aliphatic hydrocarbon radical containing from 1 to 8 carbon atoms and an alcohol of the formula HORSROH wherein R is a saturated aliphatic bivalent hydrocarbon radical and the alcohol molecule contains from 6 to 15 carbon atoms.

4. An ester of silicic acid and an unsubstituted monohydric alcohol of the formula RSOzROH wherein R is a saturated aliphatic hydrocarbon radical, R1 is a saturated aliphatic hydrocarbon bivalent radical and the alcohol molecule contains from 6 to 14 carbon atoms.

5. An ester of a thiaalkanol and silicic acid.

6. Tetrakis(7-methyl-4-thiaoctyl) silicate.

7. Tetrakis(6-methyl-4-thiaheptyl) silicate.

8. 1,6-di(trimethylsiloxy) 4-thiahexane.

9. Monomeric sulfur-containing esters of the group consisting of (1) esters of silicic acid and derivatives of silicic acid wherein at least one but not all of the OH groups has been replaced by a hydrocarbon radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, and saturated hydrocarbon monohydric alcohols having a member of the group consisting of S, SS-, SO- and SO2 attached to carbon atoms in an open-chain portion of the molecule, and (2) esters of derivatives of silicic acid wherein all but one of the OH groups have been replaced by a hydrocarbon radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, and saturated hydrocarbon alcohols having a member of the group consisting of S, SS, SO- and 40% attached to carbon atoms in an open-chain portion of the molecule.

References Cited in the file of this patent UNITED STATES PATENTS 2,386,793 Hanford Oct. 16, 1945 2,413,718 Lincoln et al. Jan. 7, 1947 2,526,506 Rogers et a1 Oct. 17, 1950 2,567,724 Moody Sept. 11, 1951 2,590,039 Richter Mar. 18, 1952' 2,592,175 Orkin Apr. 8, 1952 

1. AN ESTER OF A THIALKANOL AND AN ALKYLTRIHYDROXYSILANE. 